Dendritic spines are small protrusions from neuronal dendrites that form the postsynaptic side of most synapses in the brain. Dendritic spines undergo changes in both their morphological and electrical properties in response to repeated activity, and these changes are implicated in both learning and memory. These changes are mediated by a wide variety of signaling proteins with a complex network of interactions, and defects in this signaling network produce spines with abnormal development and regulation. Defective dendritic spines are associated with a host of mental health problems, including mental retardation, schizophrenia, and other neurological disorders. Over the past decade researchers have made considerable progress in identifying the important proteins in the signaling network, and have characterized many of their interactions. Nevertheless, there remain significant gaps in our understanding of this network. One important protein in this regulatory network is cofilin, which is responsible for regulating the spine's cytoskeleton. Cofilin is known to be regulated through two pathways: a deactivating pathway that works through LIM kinase, and an activating pathway that works through Slingshot. Only the deactivating pathway has been studied in great detail. Here we propose to study the cofilin activation pathway through Slingshot using both computational modeling and experiment. The modeling will explore the behavior of the signaling network in realistic spatial geometries and in the context of other interacting signaling and electrical processes. The experiments will be performed on mouse hippocampal slices and will involve whole-cell patch-clamp recording coupled with fluorescent imaging of the spine actin cytoskeleton and important regulatory proteins of the cofilin pathway. The modeling and experimental work will be developed simultaneously, with the model used to inform the experimental approach and the experiments used to refine and constrain the model. The proposed research training plan will provide the fellow, whose Ph.D. is in physics, an opportunity to develop skills in laboratory imaging and electrophysiological techniques while tackling an important problem in neurobiology.